This invention relates to a control system for controlling the working depth of a tractor-coupled implement as a function of various sensed and operator-controlled parameters, and in particular, to the start-up operation of such a system.
When an electrohydraulic hitch control system is turned off, the operator controls can be moved without a corresponding movement of the controlled hitch. This can cause an unexpected hitch movement when the system is repowered. A prior hitch control system is described in U.S. application, Ser. No. 873,858, filed June 11, 1986, now U.S. Pat. No. 4,677,542, a continuation of Ser. No. 578,702, now U.S. Pat. No. 4,517,158, filed Feb. 10, 1984. This system includes a startup feature wherein inadvertent hitch movement is prevented upon start-up unless the actual hitch position is matched by the position of the hitch control lever. Another prior hitch control system is described in assignee's U.S. Pat. No. 4,518,044. This system controls the tractor hitch in response to sensed and commanded draft force, sensed and commanded hitch position, sensed engine speed and sensed wheel slip. In such a system, it would also be desireable to prevent inadvertant hitch movement by preventing hitch movement upon system start-up unless certain conditions are met.